1. Field of the Invention
The present invention relates to hybrid lenses and particularly to a hybrid lens for an imaging system.
2. Prior Art
With the ongoing development of microcircuitry and multimedia technology, digital cameras are now in widespread use. High-end portable electronic devices such as mobile phones and PDAs (Personal Digital Assistants) are being developed to be increasingly multi-functional. Many of these portable electronic devices are now equipped with a digital camera. Optical lenses are a key element of digital cameras, particularly in miniaturized digital cameras where high image quality is desired.
Conventionally, lenses in digital cameras are made of glass or plastic. Plastic lenses have the advantage of lower cost over glass lenses. However, plastic lenses are generally formed by molding, and tend to have problems such as deformation and low optical precision. In particular, deformation limits the ability of a plastic lens to correct chromatic aberration, and reduces the image quality of the digital camera. In summary, single lenses made of either glass or plastic cannot meet the dual demands for low cost and high image quality of digital cameras.
Recently, so-called hybrid lenses have been developed in an effort to overcome the above problems. Conventionally, an aspherical composite layer is formed on a single lens of optical glass serving as a substrate. Hybrid lenses are commercially practical as a means for forming an aspherical lens at relatively low cost. A hybrid lens is generally produced by transferring an aspherical composite layer made of an ultraviolet-curing resin onto the surface of a single lens made of optical glass.
FIG. 2 shows a conventional means and method for forming a hybrid lens. In the method, a predetermined amount of ultraviolet-curing resin 22 is poured on a mirror-finished transfer face 21 of a die 30, in order to form an aspherical composite layer. A glass convex lens 23 is placed in the die 30, and fixed to the ultraviolet-curing resin 22 by using a support frame 24. The ultraviolet-curing resin 22 thereby covers the entire transfer face 21. Then ultraviolet (UV) rays are applied from the side of the glass convex lens 23 for a predetermined time. The ultraviolet rays propagate through the glass convex lens 23 and cure the ultraviolet-curing resin 22. Thus an aspherical composite layer is formed on the glass convex lens 23, thereby providing the hybrid lens.
The above-described method allows a hybrid lens to be produced at a relatively low cost, because the die 30 has excellent workability and durability. However, depending on the type of the optical glass used, the glass convex lens 23 may not readily allow the ultraviolet rays to pass therethrough. In some cases, an excessively long time is needed to cure the ultraviolet resin 22, and productivity is thereby reduced. For this reason, only certain types of optical glass are suitable for commercial manufacturing.
In addition, the applied ultraviolet rays tend to be focused by the glass convex lens 23. In particular, the applied ultraviolet rays concentrate toward a center of the bottom surface of the glass convex lens 23, as shown in FIG. 2. This non-uniform distribution of ultraviolet rays results in the ultraviolet-curing resin 22 being cured non-uniformly, making it difficult to produce a precise hybrid lens.
Furthermore, because the ultraviolet-curing resin 22 is formed on an outer surface of the glass convex lens 23, the ultraviolet-curing resin 22 of the hybrid lens is subject to deformation. Moreover, the curing process is suitable only for the ultraviolet-curing resin 22, and other kinds of plastic material cannot be used.
Therefore, a new hybrid lens and a method for making the hybrid lens are desired in order to overcome the above-described problems.